The present invention is directed to ink compositions. More specifically, the present invention is directed to compositions suitable for use in ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises (1) water; (2) a colorant; and (3) an additive selected from the group consisting of di-substituted guanidinium salts, wherein the substituents are alkyl groups, arylalkyl groups, or mixtures thereof.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Acoustic ink jet printing processes are also known. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. These principles have been applied to prior ink jet and acoustic printing proposals. For example, K. A. Krause, "Focusing Ink Jet Head," IBM Technical Disclosure Bulletin, Vol 16, No. 4, September 1973, pp. 1168-1170, the disclosure of which is totally incorporated herein by reference, describes an ink jet in which an acoustic beam emanating from a concave surface and confined by a conical aperture was used to propel ink droplets out through a small ejection orifice. Acoustic ink printers typically comprise one or more acoustic radiators for illuminating the free surface of a pool of liquid ink with respective acoustic beams. Each of these beams usually is brought to focus at or near the surface of the reservoir (i.e., the liquid/air interface). Furthermore, printing conventionally is performed by independently modulating the excitation of the acoustic radiators in accordance with the input data samples for the image that is to be printed. This modulation enables the radiation pressure which each of the beams exerts against the free ink surface to make brief, controlled excursions to a sufficiently high pressure level for overcoming the restraining force of surface tension. That, in turn, causes individual droplets of ink to be ejected from the free ink surface on demand at an adequate velocity to cause them to deposit in an image configuration on a nearby recording medium. The acoustic beam may be intensity modulated or focused/defocused to control the ejection timing, or an external source may be used to extract droplets from the acoustically excited liquid on the surface of the pool on demand. Regardless of the timing mechanism employed, the size of the ejected droplets is determined by the waist diameter of the focused acoustic beam. Acoustic ink printing is attractive because it does not require the nozzles or the small ejection orifices which have caused many of the reliability and pixel placement accuracy problems that conventional drop on demand and continuous stream ink jet printers have suffered. The size of the ejection orifice is a critical design parameter of an ink jet because it determines the size of the droplets of ink that the jet ejects. As a result, the size of the ejection orifice cannot be increased, without sacrificing resolution. Acoustic printing has increased intrinsic reliability because there are no nozzles to clog. As will be appreciated, the elimination of the clogged nozzle failure mode is especially relevant to the reliability of large arrays of ink ejectors, such as page width arrays comprising several thousand separate ejectors. Furthermore, small ejection orifices are avoided, so acoustic printing can be performed with a greater variety of inks than conventional ink jet printing, including inks having higher viscosities and inks containing pigments and other particulate components. It has been found that acoustic ink printers embodying printheads comprising acoustically illuminated spherical focusing lenses can print precisely positioned pixels (i.e., picture elements) at resolutions which are sufficient for high quality printing of relatively complex images. It has also has been discovered that the size of the individual pixels printed by such a printer can be varied over a significant range during operation, thereby accommodating, for example, the printing of variably shaded images. Furthermore, the known droplet ejector technology can be adapted to a variety of printhead configurations, including (1) single ejector embodiments for raster scan printing, (2) matrix configured ejector arrays for matrix printing, and (3) several different types of pagewidth ejector arrays, ranging from single row, sparse arrays for hybrid forms of parallel/serial printing to multiple row staggered arrays with individual ejectors for each of the pixel positions or addresses within a pagewidth image field (i.e., single ejector/pixel/line) for ordinary line printing. Inks suitable for acoustic ink jet printing typically are liquid at ambient temperatures (i.e., about 25.degree. C.), but in other embodiments the ink is in a solid state at ambient temperatures and provision is made for liquefying the ink by heating or any other suitable method prior to introduction of the ink into the printhead. Images of two or more colors can be generated by several methods, including by processes wherein a single printhead launches acoustic waves into pools of different colored inks. Further information regarding acoustic ink jet printing apparatus and processes is disclosed in, for example, U.S. Pat. No. 4,308,547, U.S. Pat. No. 4,697,195, U.S. Pat. No. 5,028,937, U.S. Pat. No. 5,041,849, U.S. Pat. No. 4,751,529, U.S. Pat. No. 4,751,530, U.S. Pat. No. 4,751,534, U.S. Pat. No. 4,801,953, and U.S. Pat. No. 4,797,693, the disclosures of each of which are totally incorporated herein by reference. The use of focused acoustic beams to eject droplets of controlled diameter and velocity from a free-liquid surface is also described in J. Appl Phys., vol. 65, no. 9 (May 1, 1989) and references therein, the disclosure of which is totally incorporated herein by reference.
U.S. Pat. No. 5,626,654 (Breton et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous liquid vehicle, a dye, and a vesicle-forming lipid, wherein vesicles of the lipid are present in the ink. Examples of vesicle-forming lipids include glycerophospholipids, diacylglyceroles, .alpha.,.omega.-dipolar diacetyles, and the like.
U.S. Pat. No. 5,425,805 (Botros et al), the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink composition comprising a liquid vehicle, a dye, and an N-hydroxyalkyl branched polyethyleneimine polymer or an N-hydroxyalkyl diphenylguanidine substituted at about 80% of the available nitrogens. The dye in this ink jet composition decreases the solubility of the ink and, therefore, can be used to formulate waterfast inks for ink jet printers.
U.S. Pat. No. 5,403,955 (Farooq), the disclosure of which is totally incorporated herein by reference, discloses mordants based upon a polyethyleneimine backbone and either pendant phosphonium or quaternized-nitrogen compounds. The mordants find use in stopping or controlling ink-bleeding into ink-jet receptors and photographic films.
U.S. Pat. No. 5,378,269 (Rossi et al.), the disclosure of which is totally incorporated herein by reference, discloses a recording liquid for 5. ink-jet recording comprising coloring matter, which is an image-forming component, and a liquid medium for dissolving the coloring matter therein. The liquid medium is ethanol and the coloring matter is a dye represented by the following general formula (A): ##STR1## or the following general formula (B): ##STR2## as an image-forming component.
U.S. Pat. No. 5,334,435 (Rossi et al.), the disclosure of which is totally incorporated herein by reference, discloses a recording liquid for ink-jet recording comprising coloring matter, which is an image-forming component, and a liquid medium for dissolving the coloring matter therein. The liquid medium is ethanol and the coloring matter is a dye represented by the following general formula (A): ##STR3## or the following general formula (B): ##STR4## as an image-forming component.
U.S. Pat. No. 4,840,674 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses an improved ink composition comprising a major amount of water; an organic solvent selected from the group consisting of tetramethylene sulfone; 1,1,3,3-tetramethyl urea; 3-methyl sulfolane; and 1,3-dimethyl-2-imidazolidone; which solvent has permanently dissolved therein spirit soluble dyes such as black, yellow, cyan, magenta, brown, and mixtures thereof. At least one of the specific ink compositions disclosed therein also contains diphenyl guanidinium sulfate.
U.S. Pat. No. 5,019,166 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing composition comprising a dye, a liquid medium, and a surfactant selected from the group consisting of polyoxyalkylated ethers, anionic bitail fluorothio alkyls, alkyl aryl sulfonates, alkyl amine quaternary salts, and mixtures thereof. Also disclosed is a process for generating images which comprises causing the ink compositions to be ejected from a thermal ink jet printer in imagewise fashion onto a substrate.
With respect to issues of image permanence, until recently, little attention has been paid to wet smear. Rather, waterfastness has been the most widely measured criterion of image permanence. While good wet smear characteristics may be found in waterfast inks, waterfastness of an ink does not guarantee that the ink will exhibit good wet smear characteristics. Wet smear is the mechanical displacement of the ink colorant from a receiver sheet (such as paper, transparency, or the like), subsequent to drying of the original image, when the dried image is subjected to contact with a wet object, and primarily reflects how tightly the colorant is bound to the topmost areas of the receiver sheet. Waterfastness is the degree to which water can resolvate and remove the ink colorant from the receiver sheet without mechanical assistance. Binding of the colorant is common to and important for both characteristics. Obtaining good wet smear characteristics, however, is more difficult than obtaining good waterfastness, since wet smear has an additional mechanical component thereto. A friable insoluble surface may exhibit good waterfastness but poor wet smear; accordingly, solving the problem of smear requires stabilization of the image surface, either with or without also improving waterfastness. Obtaining good wet smear characteristics is particularly difficult with yellow inks, and also particularly difficult with inks containing water soluble acid dyes or food dyes.
While known compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions suitable for ink jet printing processes. In addition, a need remains for ink compositions with improved wet smear characteristics. Further, a need remains for ink compositions containing water-soluble dye colorants that exhibit improved wet smear characteristics. Additionally, a need remains for ink compositions containing acid dye or food dye colorants that exhibit improved wet smear characteristics. There is also a need for ink compositions containing yellow acid dyes or food dyes that exhibit improved wet smear characteristics. In addition, there is a need for ink compositions containing Acid Yellow 23 dye that exhibit improved wet smear characteristics. Further, there is a need for ink compositions that exhibit improved soaking waterfastness characteristics.